Can you help me make sense of the second half of the sentence? Thanks!

Recall that "cum" has multiple uses; one is the preposition "with," but this requires the noun to be in the ablative case. You'll notice that "cibum" is accusative/nominative, so it can't be that usage. Otherwise, "cum" can have a variety of adverbial meanings, in this case, temporal. Note that the verb is in the indicative; "cum" with the indicative indicates time, as in "when" or "since". Other non-temporal uses of "cum" will probably be introduced later, but they involve the verb being in the subjunctive.